The lanthanides are a series of 15 chemical elements in the periodic table, ranging from lanthanum (atomic number 57) to lutetium (atomic number 71). These elements are known for their similar properties, including high melting points and the ability to form strong magnetic fields. They are often used in various applications, such as in strong magnets, phosphors for lighting, and catalysts in chemical reactions. The actinides are another series of 15 elements, starting with actinium (atomic number 89) and ending with lawrencium (atomic number 103). Most actinides are radioactive, with uranium and plutonium being well-known for their use in nuclear energy and weapons. These elements are typically found in nature in trace amounts and are important in fields like nuclear medicine and radiochemistry.